2014 MC or 2018 MC

Look at the build date on the tunnel near the rear bumper.
If it was built November or later, most if not all of the service bulletins were handled at production. But there could be more updates/bulletins...

Just so you know it's going to run like a complete ass for the first 20 minutes and then be a little fat for the next 5.7 hours before you get full through throttle

Depends on how u ride.
1,000 miles on my 18.
300 miles on my 19.
No issues.
Drive over logs and rocks and u may brake a chain case.
Flip over backwards (bad wheelies) probably gonna bend the tunnel.

Back to the what years were big changes thing. Lots of subtle changes over the years to get to where they are now. Here's a summary off the top of my head with regard to the 2 stroke 800:
2012 - First year of the proclimb chassis. Wasn't any lighter (maybe even heavier) than the 2011 M-series. Had less horsepower too, but much better suspension. Fit and finish was rough for a new model. Riding a 2011 M8 back to back with a 2012 the 2012 didn't do anything better off trail in my mind, but was smoother on the trail. Painted tunnels and skids on limited models.
2013 - Change from 40" ski stance to 38", 2.6" lug track replaced the 2.25" lug, front skid mount location lowered to make the sled feel lighter on its feet. Short cooler with painted tunnels and rails on limited models to reduce ice buildup on tunnel and rear suspension.
2014 - 26 (?) subtle changes from the 2013. Highlights include rear skid relocation down and back (same location as current sleds). Change in clutch heat treatment to minimized warping and belt heat generation. Short cooler and colored tunnels/skids extended through the snopro package. A bit lighter.
2015 - largely the same as the 2014.
2016 - Change to Team brand clutches greatly improved durability. 36" ski stance with revised spindles and castor angle (still used on current sleds). Revised rear skid geometry (still used on current sleds). Limiteds got Evol shocks and 3" lug tracks. Switched to 7T drivers for more track clearance, but left chaincase gearing the same so they were geared too low overall. Changed to Borg Warner chain and gear profile for greater chain case durability. Skis that didn't sink to china, but were really twitchy IMO.
2017 - Mountain Cat model was added to the lineup - Same as 2016 Limited but had 1" narrower running boards and belly pan plastic pulled in to reduce paneling out on side hills. Also first model with the lowered driveshaft and back to 8T drivers propelling the track. Bit lighter. Front suspension geometry, tunnel, bulkhead, and skid geometry the same as current sleds.
2018 - Ctec motor. Refined, slimmer body work. Deflectionless Team primary clutch. Upgraded shock package on Mountain Cat model. Aluminum driveshaft and reduced weight. Re-designed skis.
2019 - Added the alpha skid/track option. Factory tether. Nicer handlebar controls. Re-designed skis again. More HP.

With enough time, money, and parts you can make anything back to a 2012 into a 2018 with a Suzuki motor.

There 2019 hardcores and mtn cats for 1150 out the door right now and alpha1s for 12 if you look around

remember 20 min with only 7k rmp max and 4% more fuel and 10 to 1 oil

5.7 hours with 2% more fuel before she is all yours.

And 30:1 oil during the 5.7hrs.
Then ~60:1 after.

Yes

I'm 6'-2" and like 5.5"-6" riser. So yeah you'll definitely need to go taller! Not sure how far you can go with the standard cables and brake lines. The old adjustable posts used to go pretty tall. That was before they re-did the controls for 2019 though.